Smoke generator



April 14, 1959 A. F. cHARwAT SMOKE GENERATOR 2 Sheets-Sheet I 1 Fi-ledFeb. 27, 1956 April 14, 1959 A. F. CHARWAT SMOKE GENERATOR Filed Feb.27. 1956 2 sheets-shea 2 eser-ral',-

lited States Patent `2,882,240 SMOKE `GElJERTAOR Andrew F. Charwat, LosAngeles, Calif., fassignor to INorthrop Aircraft,` Inc., Hawthorne,Calif., a corporation of California ApplicatonFebruary 27, "1956,vSerial No. 567 ,786

yt Claims. (CL-252-359) The present invention relates to smokegenerators for 'use in examining the-dow of a gaseous lluild overairfoils or 'other bodies positioned in` a 'stream of said huid, and isof :the type producing a visible vapor condensation or fog asdistinguished from the use of fumes or clouds of dust.

The usual use of such generators is to introduce smoke into a windtunnel in whichfan' a'irfoil is suspended, in order to 'examine throughwindows "in the wall of 'the tunnel, `the character Yof the air ilow'over the airfoil surface. Such apparatus are of increasing importanceas the speed of airplanes increases and vintensive study is beingmade ofmeans to maintain a close adherence ofthe airstream to the" surface ofthe 'airfoil at the high speeds. y l

The ""smoke should be dense and v'clearlyvisible,uniform in` qualityduring extended'runs, have good permanence in the airstrea'm,4benoncorrosive, nontoxic, and 'be free from depositsfwhich" clog narrowpassages.

.The apparatus by which the `smoke is produced should bersimpl'e andreliable, automatic in action, capable of wide variation in the amountofsatisfactory smoke produced as may be required, from a thin-filamentto' the large quantity required to make visible an eXtend'edeld of dow.Y

The' design of a satisfactory smoke generator to meet the requirements'mentioned provides severall problems. The most suitable material hasbeen found to be a heavy mineral oil which .is heated to Ydrive offvapor which is mixed with air to produce smoke by condensing the oilvapor into minute `droplets of about inneren in diameter. f

In known types of smoke `generators A'using he'avy'oil vapor the 'oilwas boiledk and the vapor exhausted through a small oriiice'before being'mixed withjet's of air, but resultant condensation of' the hot` oil atthe orilice was a source of trouble. l A v e The rate of production ofthe oil vaporshould be con-y stant, requiring' a constant level of theoil in the heater, a constant rate of heating the oil and avoidance `ofvariation of conditions in the heater. In previously suge gestedapparatus variation in the heater is` caused by injecting vapor from a`jet into a stream of air, which yis the only adjustable element withresultant variation of the smoke produced. e

Inorder to meet the requirements above outlined of a satisfactory smokegenerator, itis an object of theinven'- tion'toprovide a heating vessel`in which oil is heatedat a, constant rate' to' a temperature well belowthe boiling point of the oil and to keep allparts of the generator belowthat temperature. Y

lt is a further object'of thel invention to lprovide for removing thevapor produced by heating'th'e o-il by playing cool air on the heatedsurface of the oil in the heater, to condense the vapor and remove the'resulting 'sinoke through tubes of relatively large diameter, thusavr'idingV the use of narrow oriiices through which the vapor isejected.

. loe

2 A'further object of the invention is to provide a smoke generatorcapable of as wide variation in the amount of smoke fproduced` as may berequired without variation in the quality, of the smoke.

A`Another Vobject of the invention is to provide a smoke generator whichis lexible in adjustment,l enabling the economical working of the deviceyat good elliciency under a variety of conditions.

-A `still further object of the invention is to provide a smokeYgenerator capable of prolonged use without the need of disassembly forcleaning, thus reducing the idle time ofthe device.

Ano'ther object of the invention is to provide a method for producingsmoke from heated loils maintained below their boiling point. A

Still further objects and Afeatures of the invention will appearifromthe following speciiication read with reference to the accompanyingillustrative drawings.

In the drawings: l e

"Figure 1 is a front elevation of the device of the invention; x

Figure `2 is across section, drawn on a reduced scale, on the line "2 2in Figure `l; and l Figure 3 isY a schematic diagram majking clear thearrangement of 4the various components of the device.

It should be noted that in the form illustrated the `device is intendedto supply smoke to a small wind tunnel i'n which ininiature models ofVair foils and the like are tested. e

"Referring no'v'v lto Figure yl, the vnumeral 10 indicates a casecontaining thesmoke generator, this case comprises side walls 11 and 12,a base 13, top 14, and a front panel 1S carrying control valves andswitches, 'but` both "front and 'back ''f 'the ease 10 'are apen tofacuitate access to various components of the device for reasons whichwill'later appear. i

The components of the device comprise a 'reservoir 16 for the `oilusedto supply the smoke, the reservoir being provided with an imper'foratefiller cap `17 and oil shut-off valve 18 operated by handle 18a, whichcontrols the oil supply to a constant level control means 1'9. The means19 vcomprise a transparent, tubular, valve housing body 20, ofy'mol'ded'Pyrenfor example, formed with'ilanges 21 Vand 22. rnnge 21 is' clampedby end plate 23 to plate Y2.4 'on which the lvalve '|18 is mounted, andvilange 22`iscla'n'1ped between 'plate 25 arid plate 2:6 to which anoil' delivery tube is braz'ed. The oil in housing 20 is maintained at aconstant level by'iloat 28 acting on a spring loaded 4oil inlet vvalve29. The levelofthe oil is indicated bythe `dashed line 30.

Tube 27 delivers; the oil tothe heating unit generally metal wan 3'2,the oilbei'ng towed in a thin Sheet through the heating unit, in theembodiment shown, by arranging the cylindrical body 33 of athermo-switch coakially in the heater and supplying 'the 'oil ytol therelatively narrow spacei34 between the outer surface of the body 33 andinner wall lof the'heater. The housing Z0, yheater 31 and connectingconduit form a U`shaped container so that if the pressure on keach end4is equal, the level of the liquid inthe housing will be the same asthat of the liquid in the heater. e e i Heating coils 35 andV 36arewound around the outer periphery ofthe heater, these coils havingequal values of resistance and being arranged so that they may beconnected in series or parallel, as indicated 'in Figure 3, by

' switch 37. Thermo-switch 33 is of the make or break type and may beadjusted to operate at any value between and 400 F.' by settingwheel 38.The electrical elements will be further referred to later.

`Aii'e'at retaining jacket 39 is placed over the heating coils. A jetring 40 or vapor condensing' chainber mounted above the heater 31, andheat transfer to it from the heater is reduced by an asbestos washer(not shown) or the like and by a wire screen 42 mounted in the heater atthe level 30 of the top of the oil therein. The jet ring 40 is coveredby a cap 43, a second screen 44 being mounted between the top of the jetring 40 and the cap 43. A smoke unrestricted outlet 'conduit 45. leadsfrom the cap to a collector vessel later decribed.

Air under low pressure is supplied to the jet ring 40 through air inlet46, shut-olf valve 47 and pipe 48 to a valve body 50, which is manuallyadjusted by knurled wheel 51 to control ow to a series of jets suppliedby small diameter tubes, for instance 2 as shown at 52, 53, which injectthe air into the jet ring above the top of the oil. A second valve 54 isarranged to enable one jet or both jets to be supplied with air, or bothjets shut ofI.

The remainder of the air flows through tubes 55 leading air from theouter shell of the valve and over the length of the tubes 52, 53 of thejets and exhausting into the space around the jet ring 44, thus aidingin keeping it cool.

A further path for air entering valve S is provided by a tube 56 leadingto the collector vessel above referred to and for a purpose laterdescribed.

It is to be noted at this point that the oil heated in the heater is notboiled but that the vapor given olf by the heated air is condensed tosmoke by the cool low pressure air delivered by the jets, theconstruction being such as to keep the smoke cool.

The oil reservoir 16, oil valve housing 19 and the jet ring 40 aremaintained at a common pressure by tubing' 57 and a small condensatetrap 58 is provided to trap any vapor condensed in the tubing.

The smoke owing through outlet 45 is led to the collector and settlingvessel 59 from which it is discharged through the unrestricted dischargetube 60 for use.

A regenerator or feed-back arrangement is preferably provided to improvethe quality of the smoke especially at very low ilow rates. Theregenerative arrangement comprises the tube 56, the air flowing throughwhich is controlled by the on-oi valve 61, and delivers air from itsnozzle end 62 into the belled end 63 of feed-back tube 64, with aninjector elect which pulls some of the smoke out of the collector vessel59. The smoke flow in tube 64 is also controlled by valve 61 and isdelivered into valve 54 through jet 65 and mixes with the air passing tothe jets and into the jet ring 40, the recirculated air and smoke beinga considerablefraction of the pure air injected into the jet ring.

The regenerative action improves the quality of the smoke particularlyat low ow rates both by maintaining circulation even at minimum rates ofsmoke production and also is believed to increase the amount ofsmokeformation by providing already formed particles of condensed vapor asnuclei for facilitating the formation of smoke particles.

The circuit by which electric current is supplied to both thethermoswitch 33 and the heating coils comprise a plug in socket (notshown) and to which a cable shown at 67 is connected. Lead 68 isconnected through the make-or-break thermoswitch 33 to contact arm 69 ofmovable contact operating bar 70 of insulating materialy positionl whichmay be moved to either high or low from off position by the small handle71. Lead 72 is connected between contact 73 and a connection at the midpoint of heating coils 35, 36. Contact 74l is connected by lead 75 tothe lower end of coil 35. Switch arm 69 may be brought into engagementwith either contacts 73 or 74. A second contact 76 is connected by lead77 to lead 75. A lead 78 is connected to the upper end of heating coil36 and to the opposite side of the line. A second contact arm 79 ismounted on contact operating bar 70 and thus moves in unison withcontact yarm 69. l

perature which will be below boiling point of the oil,

Arm 79 is connected to lead 78 and engages contact 76 when contact arm69 engages contact 73 thus completing parallel circuits for coil halves35 and 36. When arm 69 engages contact 74 a circuit is established inthe coil halves 35, 36 which then are in series. The circuit arrangementenables a greater amount of heat to be supplied to the oil heater whenheating the oil to start the device thus cutting down starting time and,after generation of smoke has been stabilized, enables the apparatus tocontinue in operation with lesser amount of heat. A manually operatedmaster switch 80 enables electric current to be cut olf or supplied tothe apparatus, and a pilot light 81 indicates when the electric currentis turned on by the switch.

A satisfactory oil for use in the device is a paraiin boiling at 460 F.,the thermoswitch being set at about 400 F. so that boiling of the oilcannot occur. The small smoke generator described which measures about15 inches in width, 18 inches in height and 8 inchesin depth, and istherefore readily transportable, can produce a density of about 10gsmoke particles per cubic inchl and can be adjusted to deliver from .25cubic inch to 2 cubic inches of smoke with an input of some 250 watts atlower power.

The cool smoke produced and the relatively large diameter tubes throughwhich it is conducted reduce condensation of the smoke to a minimum andsuch as occurs causes no clogging of the passages.

The use of air at a constant low pressure and the equalization of thepressures in the oil supply tank, float valve housing and oil vapor orjet chamber, with the maintenance of the oil at a substantially constanttemensures steadiness of the smoke generation and freedom frominterference from variations of pressure either within the apparatus ordue to outside causes. I I

The flexibility of output without variation 1n quality of smoke orinstability in rate of smoke generation is believed to be much betterthan that obtained by previ ously proposed devices.

While in order to comply with the statute, the lnvention has beendescribed in language more or less specificl as to structural features,it is to be understood that the invention is not limited to the specificfeatures shown, but that the means and construction herein disclosedcomprise a preferred form of putting the invention into eifect, and theinvention is therefore claimed in any of its forms' or modificationswithin the legitimate and valid scope of the appended claims.

What is claimed is: 14. In vapor or smoke generating apparatus, thecombination comprising: a liquid heating chamber; means adapted tosupply liquid and heat to said heating cham-. v` ber; a thermostat insaid heating chamber adapted toI maintain the temperature of liquid inthe latter below the boiling temperature of said liquid; a vaporreceiving. chamber contiguous with and arranged above said heat-i ingchamber; unrestricted conduit means adapted to con# vey vapor from saidvapor receiving chamber; a first, metal screen positioned at the top ofsaid heating chamber to provide a perforated partition between thelatter and said vapor receiving chamber; tubes adapted to deliver a coolgaseous medium into said vapor receiving chamber in a direction toimpinge on said first screen;

first conduit means adapted to deliver al gaseous mediumto saidapparatus; second conduit means communicatingv with said rst conduitmeans and staid tubes; and valve.A

. means adapted to direct a portion of said gaseous medium owing throughsaid second conduit means to said tubes andthe remainder against theoutside walls of said vapor collecting chamber.

2. Apparatus as set forth in claim 1 and in addition in `cluding asecond wire screen arranged in said vapor collecting chamber between thearea of introduction of, cool gaseous medium thereinto and theunrestricted l.

conduit means leading condensed vapor or smoke out of the apparatus.

3. Visible vapor or steam generating apparatus comprising: a liquidheating unit; means supplying liquid and heat to said unit; said unitincluding a chamber receiving vapor from said unit; a thermostat mountedin said unit and adapted to maintain the heat of said liquid below theboiling point thereof; means maintaining said vapor receiving chamber ata relatively low temperature; means injecting a gaseous medium underpressure and at a lower temperature than said vapor into said vaporreceiving chamber; unrestricted conduit means leading the vaporcondensed in said vapor receiving chamber out of the unit for usc; asettling vessel into which the coudensed vapor or smoke from the vaporreceiving cham ber is led; unrestricted conduit means leading thecondensed vapors or smoke from said settling chamber out of theapparatus for use; and means for recycling a portion of the condensedvapor or smoke from the settling chamber into the gaseous mediumintroduced into the 20 vapor receiving chamber.

4. Apparatus as set forth in claim 3 in which said means for recycling aportion of the condensed vapors or smoke comprise: an injectorpositioned in said settling chamber; a conduit leading gaseous mediumunder pressure to said injector; conduit means leading from saidinjector to lead smoke injected therein to the conduit leading gaseousmedium into said vapor receiving chamber; and valve means controllingthe conduits for recycling a portion of the smoke Treating Oil FieldEmulsions, Petroleum Industry Series (Voc. Training Course), 1949, Amer.Petrol. Inst., Austin, Tex., page 86.

1. IN VAPOR OR "SMOKE" GENERATING APPATATUS, THE COMBINATION COMPRISING:A LIQUID HEATING CHAMBER; MEANS ADAPTED TO SUPPLY LIQUID AND HEAT TOSAID HEATING CHAMBER; A THERMOSTAT IN SAID HEATING CHAMBER ADAPTED TOMAINTAIN THE TEMPERATURE OF LIQUID IN THE LATTER BELOW THE BOILINAGTEMPERATURE OF SAID LIQUID; A VAPOR RECEIVING CHAMBER CONTIGUOUS WITHAND ARRANGED ABOVE SAID HEATING CHAMBER; UNRESTRICTED CONDUIT MEANSADAPTED TO CONVERY VAPOR FROM SAID VAPOR RECEIVING CHAMBER; A FIRSTMETAL SCREEN POSITIONED AT THE TOP OF SAID HEATING CHAMBER TO PROVIDE APERFORATED PARTITION BETWEEN THE LATTER AND SAID VAPOAR RECEIVINGCHAMBER; TUBES ADAPTED TO DELIVER A COOL GASEOUS MEDIUM INTO SAID VAPORRECEIVING CHAMBER IN A DIRECTION TO IMPINGE ON SAID FIRST SCREEN FIRSTCONDUIT MEANS ADAPTED TO DELIVER A GASEOUS MEDIUM TO SAID APPARATUS;SECOND CONDUIT MEANS COMMUNICATING WITH SAID FIRST CONDUIT MEANS ANDSTAID TUBES; AND VALVE MEANS ADAPTED TO DIRECT A PORTION OF SAID GASEOUSMEDIUM FLOWING THROUGH SAID SECOND CONDUIT MEANS TO SAID TUBES AND THEREMAINDER AGAINST THE OUTSIDE WALLS OF SAID VAPOAR COLLECTING CHAMBER.